I just recieved mine today and it's fantastic quality, especially for DealExtreme, who sell the odd bit of p!ss poor sh!te, lol.
It's a two part snap on shell/casing with no dismantling of your DS, took me only moments to fit. It fits like a glove and does not budge once on. Also, It does not interfere with the functioning of the DS while playing. It has a very tactile silicone ultra matt finish, and does not show fingerprints, hairs, dust etc like the original finish of the DS lite does, and looks much better for it. It is quite a thick casing, so should offer some decent protection from knocks etc.
The pics on DealExtreme show the casing with writing on it and a 2009 date, mine has none of this thankfully, just the Jack face on the top screens casing, and the chest/crossed arms on the main body of the DS.
These are my overall impressions of the shell/casing. It's a great deal in my opinion. I'm just about to order a few more as presents for friends/family etc ;-)